Emergency brake assembly for motor-driven tool and method for operating emergency brake assembly

Abstract

An emergency brake assembly (82) for a motor-driven tool is described. The emergency braking assembly comprises a retaining structure (35); a brake element, in particular a brake cam, movably mounted on the retaining structure (35); and a linear actuating element (34) comprising a shape memory alloy (36). A first end (34a) of the actuation element (34) is attached to the retaining structure (35). A second end (34b) of the actuation element (34) is drivingly coupled to the braking element. The invention also relates to a method for operating an emergency brake assembly (82). The braking element is moved by means of an actuating element (34), and then a kinematic coupling between the actuating element (34) and the braking element is cancelled or terminated.

Description

Technical Field

[0001] The present invention relates to an emergency brake assembly for a motor-driven tool.

[0002] The invention also relates to a method for operating an emergency brake assembly. Background Art

[0003] Motor-driven tools comprising emergency brake assemblies are known from the prior art. So are emergency brake assemblies. These emergency brake assemblies are used to stop a cutting element of the tool, such as a saw blade, when there is a risk of contact between the user and the cutting element during operation or when such contact is detected. In this way, injuries are avoided or their severity is reduced.

[0004] In this respect, an actuator having an actuating element comprising a shape memory alloy can be used. The function of such an actuator is based on a thermally activated lattice transformation of the shape memory alloy, which results in a change in the length of the actuating element. An "actuating element" is therefore understood to be an element of the actuator by means of which a movement is produced, which movement is required for the actuator to act on the system actuated by the actuator, in this case a brake system or a brake element. The actuating element comprising a shape memory alloy is usually formed as a wire which shortens due to the thermally activated lattice transformation.

[0005] Such an actuator is preferably used in a reversible emergency brake assembly, ie an emergency brake assembly that can be used multiple times to stop the cutting element. It should be understood that in the case of a reversible emergency brake assembly, the actuator must be able to be actuated multiple times with the same high reliability level. Summary of the invention

[0006] It is therefore an object of the present invention to further improve an emergency brake assembly whose actuating element comprises a shape memory alloy.

[0007] The above-mentioned purpose is achieved by an emergency brake assembly for a motor-driven tool, which comprises a holding structure; a brake element movably mounted on the holding structure, in particular a brake cam or a pressure piece; and a linear actuating element comprising a shape memory alloy. The first end of the actuating element is fastened to the holding structure. The second end of the actuating element is drivingly coupled to the brake element. In this regard, a "linear actuating element" is understood to be an actuating element that can be substantially only subjected to tensile loading (i.e., can only transmit tensile forces). Such an actuating element is unstable when subjected to compressive loading. In addition, linear means that the actuating element is much longer than its width. For simplicity, a linear actuating element comprising a shape memory alloy is also generally referred to as a shape memory alloy wire or SMA wire. In the present case, the holding structure is, for example, formed by an actuator housing (i.e., by a housing of an actuator comprising the actuating element) or a brake caliper or a combination thereof. The second end of the actuating element is drivingly coupled to the brake element, which means that the brake element can be driven via this coupling, i.e., it can be moved at least from a release position in which the brake element has no braking effect to a braking position in which the brake element has a braking effect. The movement of the brake element from the release position to the brake position is preferably caused by a contraction or tightening of the actuating element. Thus, the actuating element drives the brake element. This configuration is simple and robust. In particular, this configuration is structurally simpler than the design of an emergency brake assembly in which only the release of the movement can be controlled by means of an actuating element comprising a shape memory alloy.

[0008] In summary, therefore, an "emergency brake assembly" is understood to mean a combination of an actuator and a brake element. In the present case, the actuator comprises an actuating element, which comprises a shape memory alloy. The brake element is, for example, a brake cam or a pressure piece. Such an emergency brake assembly can be part of an emergency brake unit, which is configured to brake a cutting element of a motor-driven tool until it stops.

[0009] In connection with the present invention, a "brake cam" is understood to mean a brake element which is at least partially eccentric and rotatably mounted, so that the brake element can be moved by rotation from a release position in which the brake element has no braking action into a braking position in which the brake element has a braking action. In contrast, a pressure piece can be mounted pivotably or translatorily displaceably.

[0010] It will be appreciated that the actuating element may comprise an insulating element at its end in order to electrically insulate the actuating element from the holding structure and / or from the brake element.

[0011] In one example, the holding structure is made of a synthetic material. In this case, it is not necessary to provide an insulating element on the first end of the actuating element.

[0012] According to an alternative, the second end of the actuating element is fastened to the brake element. Thus, in this alternative, the actuating element is fastened to the holding structure and also to the brake element. Thus, the brake element can be driven directly by means of the actuating element. This design is particularly simple and robust.

[0013] According to another alternative, the second end of the actuating element is coupled to the brake element via at least one intermediate element. Thus, at least one intermediate element is arranged between the brake element and the second end of the actuating element, so that the brake element can be driven by means of the actuating element and via the intermediate element. On the one hand, such an intermediate element can be used to bridge the geometric distance between the second end of the actuating element and the brake element. On the other hand, the intermediate element can also be used to convert the movement of the second end of the actuating element so that a specific movement drivenly applied to the brake element can be distinguished from the movement of the second end of the actuating element. In this case, the intermediate element can also be understood as a gear element. Therefore, the intermediate element provides a degree of freedom for adjusting the movement of the brake element when actuated by means of the actuating element.

[0014] At least one intermediate element may comprise a slide which is movably mounted on the holding structure. The slide is thus driven by means of the actuating element. The slide, in turn, drives the brake element directly or indirectly. The slide is a structurally simple and reliable intermediate element, which can thus drive the brake element in a reliable manner.

[0015] In one example, the slide is made of a synthetic material. Therefore, it is not necessary to electrically insulate the second end of the actuating element from the slide. In addition, such a slide is relatively light, but still strong.

[0016] The slide can be mounted on the holding structure in such a way that it can be moved in translation via the sliding guide. In other words, the slide is guided in translation on the holding structure. In this respect, since the holding structure can be designed to be mechanically stable, the slide is also mounted in a reliable and mechanically stable manner. Such a configuration is therefore mechanically robust.

[0017] The slide can also be mounted on the holding structure in a manner that it can be moved via at least one articulated arm. In this alternative, the slide is also mounted in a reliable and mechanically stable manner. In this regard, the articulated arm can be rigid and can be coupled to the holding structure and also to the slide via a local joint. Alternatively, the articulated arm can be formed as a solid articulated arm. In this example, the joint can be considered to be non-localized, because some parts of the articulated arm provide the articulation function, but not a specific component or element.

[0018] In another embodiment, the slide is connected to the holding structure via an elastic support element. If the slide moves, the elastic support element is elastically deformed. In this alternative, the slide is also mounted on the holding structure in a simple and robust manner. The elastic support element also has the advantage that an initial position can be assigned to the slide, in which the elastic support element is, for example, not deformed. The support element can be configured so that in the absence of external forces, the elastic support element returns the slide to this initial position.

[0019] In one example, the elastic support element is formed as a leaf spring element. In another example, the elastic support element is formed as a diaphragm spring. In another example, the elastic support element is formed as a helical spring element.

[0020] At least one intermediate element can include a push rod or an actuating pin with a brake element side end. The brake element side end of the push rod or the actuating pin is located on the brake element or can be placed on the brake element. Therefore, in this example, the brake element is driven by the push rod or the actuating pin. This is structurally simple and robust. In particular, the compression force can be applied to the brake element in a reliable manner by means of the push rod or the actuating pin.

[0021] In one example, the push rod or actuator pin is made of a composite material.

[0022] Preferably, the brake element side end of the push rod or actuating pin is separated from the brake element via a tensile force or can be separated from the brake element via a tensile force. In this example, at least in one operating situation, preferably in all operating situations, no tensile force can be applied to the brake element by means of the push rod or actuating pin. However, preferably, the compressive force can be transmitted to the brake element by means of the push rod or actuating pin. With this configuration, on the one hand, the brake element can be driven by the compressive force in a reliable manner by means of the push rod or actuating pin. On the other hand, the separation or separation ability of the tensile force also allows the push rod or actuating pin to move independently of each other relative to the brake element, and vice versa. This is particularly advantageous when the brake element is designed to be self-reinforced, so it only needs to contact the cutting element to be braked, and the further movement of the brake element is caused by the contact between the brake element and the cutting element, that is, the actuating element is no longer needed for this. Simply put, with this configuration, the brake element can be pushed by means of a compressive force. Then, the brake element and the push rod or actuating pin can move independently of each other. As far as the actuating element or the actuator to which it belongs is concerned, the separation or separation capability by the tensile force ensures that the actuator or the actuating element returns to an initial position corresponding to the release position of the brake element, wherein the brake element remains in the brake position. This provides in particular reliable protection for the actuator or the actuating element from load peaks caused by the engagement of the brake element. As a result, a high level of reliability and a long service life of the actuator and the actuating element are achieved.

[0023] In one example, the brake element side end of the push rod or the actuating pin can be located between the first end of the actuating element and the second end of the actuating element in a direction parallel to the actuating element. Thus, the brake element side end of the push rod or the actuating pin is located near the actuating element. In this way, a compact design of the emergency brake assembly is produced, because the brake element side end of the push rod or the actuating pin does not enlarge the emergency brake assembly in a dimension corresponding to the direction of the actuating element from the actuating element. In short, the brake element side end of the push rod or the actuating pin does not protrude beyond the length of the actuating element.

[0024] According to one variant, the push rod or the actuating pin has a central axis which extends parallel to the actuating element. In this respect, the central axis of the actuating pin may also be referred to as the "pin axis" and the central axis of the push rod may be referred to as the "push rod axis". This allows the forces acting in the actuating element and the forces acting in the push rod or the actuating pin to extend parallel. This is advantageous from a mechanical point of view.

[0025] The center axis of the push rod or the actuating pin can be spaced apart from the actuating element. Therefore, the center axes are preferably arranged in a parallel offset manner. The resulting design is advantageous in terms of force and is also compact.

[0026] The push rod or the actuating pin can be guided on the holding structure. The push rod or the actuating pin is thus guided in a reliable and robust manner. In particular, the guiding takes place longitudinally, i.e. along the central axis of the push rod or the actuating pin. At the same time, the guiding can be configured to prevent the push rod or the actuating pin from tilting. In this respect, the actuating pin or the push rod is preferably guided near its brake element side end, for example in the half of the actuating pin or the push rod facing the brake element. In this way, by means of the guidance on the holding structure, a particularly precise position and / or movement of the brake element side end can be achieved, so that the brake element can be actuated horizontally with high precision.

[0027] In one example, the push rod or the actuating pin is guided in a guide channel formed on the holding structure. A through hole or a through bore is an alternative to a guide channel. From a structural and manufacturing point of view, this kind of guidance is particularly simple.

[0028] Advantageously, the brake element-side end of the actuating pin or push rod is rounded. Thus, even in the case of a relative position between the actuating pin or push rod and the brake element that is impeded by tolerances, forces can be transmitted from the actuating pin or push rod into the brake element with a high level of reliability. In particular, force peaks resulting from a relative position that is impeded by tolerances are avoided by the rounded end. As a result, the emergency brake assembly as a whole operates in a particularly robust manner.

[0029] In one example, the push rod or actuating pin has a cylindrical basic shape. From a manufacturing perspective, such an actuating pin or push rod is particularly simple.

[0030] The actuating element side end of the push rod or the actuating pin can be coupled to the sliding member. Therefore, in this example, the sliding member and the push rod or the actuating pin are arranged as intermediate elements. For example, the coupling between the sliding member and the actuating pin or the push rod is rigid, that is, it can transmit compressive forces and tensile forces along the central axis of the push rod or the actuating pin. In addition, this rigid coupling can transmit lateral forces. Alternatively, the coupling can also be configured so that only compressive forces can be transmitted. In all variants, a reliable coupling is established between the sliding member and the actuating pin or the push rod, that is, a reliable drive coupling is established between the actuating element and the brake element.

[0031] In one exemplary embodiment, the actuating element is guided by means of a guide element. In this way, an expansion of the actuating element is at least partially prevented. Thus, the actuating element is protected from undesired damage.

[0032] For example, the guide element is formed as part of the holding structure, in particular as part of the actuator housing and / or the brake caliper. A compact design results.

[0033] The emergency brake assembly may also include a spring element, by means of which the actuating element is directly or indirectly spring-loaded in a direction corresponding to the tensile loading of the actuating element. Therefore, the actuating element is tensioned by means of the spring element. Therefore, the shortening of the actuating element can be used directly and accurately to drive the brake element. In particular, undesirable clearances in the drive coupling between the actuating element and the brake element are prevented. In addition, this spring loading ensures that the actuating element reliably and accurately returns to the non-actuated state after actuation. It should be understood that, in the case of providing a sliding member or a push rod or an actuating pin, the spring element can be supported on the sliding member, the push rod or the actuating pin. Alternatively or additionally, the spring element is supported on a retaining structure and / or on a guide element.

[0034] The spring element can at least partially surround the push rod or the actuating pin around the circumference. Alternatively or additionally, the spring element and the push rod or the actuating pin can be arranged coaxially. Thus, a compact design of the emergency brake assembly is produced. In addition, the tilting moment that may be generated by the spring loading is reduced.

[0035] In a variant, the spring element at least partially surrounds the actuating element around the circumference. Thus, a compact design of the emergency brake assembly is also produced. Furthermore, in this way, a purely axial spring loading of the actuating element is facilitated.

[0036] In one example, the holding structure is formed by the actuator housing and / or the brake caliper. Thus, the actuating element is fastened to the actuator housing and / or the brake caliper. Such a design is simple and may be compact.

[0037] In an example in which the retaining structure is formed by the actuator housing rather than by the brake caliper, the actuator comprising the actuator housing and the actuating element can be releasably attached to the brake caliper. A common tool may be required for this purpose. Thus, the actuator can be separated from the brake caliper and replaced as required, for example in the event of a defect. Such a configuration is therefore maintenance-friendly.

[0038] In addition, a control unit for the actuating element can be at least partially integrated into the actuator housing. This also results in a space-saving design of the emergency brake assembly.

[0039] According to one embodiment, a first sleeve is arranged on the first end of the actuating element, and the first end of the actuating element is fastened to the holding structure via the first sleeve. The actuating element can be fastened to the holding structure in a simple and reliable manner by means of the sleeve. In addition, the sleeve can comprise an electrically insulating material as required, so that the sleeve is an electrically insulating element or comprises an electrically insulating element.

[0040] According to another embodiment, a second sleeve is provided on the second end of the actuating element, and the second end of the actuating element is drivingly coupled to the brake element via the second sleeve. The actuating element can be fastened to the brake element or the intermediate element in a simple and reliable manner by means of the sleeve. In addition, the sleeve can comprise an electrically insulating material as required, so that the sleeve is an electrically insulating element or comprises an electrically insulating element.

[0041] The first sleeve and / or the second sleeve can be injection molded onto the actuating element. In this way, the sleeve can be produced and attached to the actuating element in a simple and cost-effective manner. Due to the injection molding process, no further assembly steps need to be performed to attach the first sleeve and / or the second sleeve.

[0042] Preferably, the length of the actuating element is smaller than the dimension of the emergency brake assembly in a direction parallel to the length of the actuating element. Alternatively or additionally, the length of the actuating element lies entirely within the dimension of the emergency brake assembly measured parallel to the length of the actuating element. Thus, the length of the actuating element does not determine the maximum outer dimension of the emergency brake assembly. Thus, by using an actuating element, a relatively compact emergency brake assembly can be produced.

[0043] A part of the actuating element and / or the retaining structure can mechanically shield the drive coupling part of the brake element. In this respect, "drive coupling part" is understood to mean a part of the brake element to which the second end of the actuating element is fastened or at which an intermediate element (e.g. a push rod or an actuating pin) contacts the brake element. Thus, if the emergency brake assembly is viewed from the outside, the drive coupling part is positioned further within the emergency brake assembly than the above-mentioned part of the actuating element and / or the retaining structure. Thus, protection against a human hand being embedded in the drive coupling part and protection against the ingress of foreign objects are provided.

[0044] In another example, at least a portion of the actuator housing can mechanically shield the drive coupling portion of the brake element. Thus, if the emergency brake assembly is again viewed from the outside, the drive coupling portion is located further inside the emergency brake assembly than the actuator housing. As a result, protection against a human hand being inserted into the drive coupling portion and protection against the ingress of foreign objects are again provided.

[0045] The above objects are also achieved by a method for operating an emergency brake assembly having a movably mounted brake element for braking a cutting element of a motor driven tool. The emergency brake assembly also includes a linear actuating element comprising a shape memory alloy. The actuating element is drivingly coupled to the brake element. The method comprises:

[0046] - moving the brake element by means of the actuating element, and

[0047] The movement coupling between the actuating element and the braking element is subsequently cancelled or terminated.

[0048] In particular, by means of this method, the brake element is moved so that it contacts the cutting element to be braked. In this case, the brake element can apply a desired braking action. In another preferred manner, the brake element cooperates with the cutting element in a self-reinforcing manner. This means that due to the interaction between the brake element and the cutting element, the braking action (for example, in the form of a braking torque) generated when the brake element and the cutting element first contact is further increased. For example, this is possible when the brake element is designed as a brake cam or a pressure piece mounted in an articulated manner. Utilizing this method, a relatively compact and relatively inefficient actuating element may be sufficient to achieve a relatively strong braking action in a reliable manner. Canceling or terminating the mobile coupling prevents the undesirable mechanical influence from the brake element from reacting in the actuating element.

[0049] The concept forming the basis of the method according to the invention can be summarized simply as follows: the brake element is only struck or pushed by the actuating element in the direction of the cutting element until the brake element contacts the cutting element. Then, the actuating element is separated from the brake element so that the brake element can be further moved in the direction of the braking position independently of the actuating element. At the position where the cutting element has just been braked by the actuating element or has been braked to its stop position, the intermediate element (e.g., push rod or actuating pin) optionally provided is separated from the brake element, i.e. spaced apart. In a variant in which the actuating element is directly fastened to the brake element, separation is achieved in the following manner: at the position where the cutting element has just been braked by the actuating element or has been braked to its stop position, the actuating element presents a state in which it can no longer affect the movement of the brake element or can only affect the movement of the brake element to a lesser extent. For example, the actuating element is loose in this respect. The separation of the actuating element from the brake element also ensures that the operating displacement of the drive coupling part of the brake element (i.e., the moving distance traveled by the drive coupling part when actuated) can be greater than the operating displacement of the actuating element. Thus, an actuating element having a relatively small operating displacement can be combined with a braking element having a relatively large operating displacement.

[0050] It will be appreciated that the method according to the invention can be performed by means of the emergency brake assembly according to the invention.

[0051] According to a variant, the method also comprises returning the actuating element to the initial position, wherein the return takes place independently of the braking element. Thus, the return of the actuating element may already take place while the braking element is still in the braking position. The braking element can then also be returned at a later time. In this way, it is ensured that the actuating element is ready for use again as quickly as possible after its actuation.

[0052] The above object is also achieved by a method for operating an actuator of an emergency brake unit of a motor-driven tool. The actuator comprises an actuating element, which comprises a shape memory alloy. The actuating element is coupled to at least one electrical energy storage unit via an electrical switching element, so that by actuation of the switching element, the actuating element can be selectively supplied with electrical energy stored in the energy storage unit. The method comprises:

[0053] - detecting or obtaining an environmental parameter and / or a first operating parameter of the actuator and / or a second operating parameter of a tool equipped with the actuator, and

[0054] - operating the actuator in dependence on the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter.

[0055] In this regard, the designation of the first operating parameter and the second operating parameter is only used to be able to better distinguish the operating parameters of the actuator and the operating parameters of the tool equipped with the actuator. Multiple operating parameters are not implied. Therefore, the method according to the present invention takes into account the environmental parameters describing the environment in which the actuator of the emergency brake unit operates and / or the first operating parameters characterizing the operating state of the actuator and / or the second operating parameters characterizing the operating state of the tool equipped with the actuator. Since the actuator is operated according to the environmental parameters and / or the first operating parameters and / or the second operating parameters, it is ensured that the actuator can always operate with constant operating characteristics, regardless of the changes in the environmental parameters and / or the first operating parameters and / or the second parameters. Therefore, the actuator works reliably independently of the environmental parameters and / or the first operating parameters and / or the second operating parameters. Of course, this even applies to the case where the actuator is actuated multiple times. It should be understood that the actuator can only be operated according to the parameters that have also been previously detected or obtained. Therefore, in detail, it can be ensured that a current is supplied to the actuator element at each actuation, and the current has a sufficient magnitude to achieve a safe and reliable actuation of the actuator. In particular, a sufficiently fast actuation of the actuator is achieved. At the same time, however, the current can be chosen to be low so as to avoid excessive aging or even damage to the actuator. A low amount of current means a low thermal load on the shape memory alloy. This leads to a relatively slow aging. Thus, the actuator operated by the method according to the invention has a high level of reliability and a long service life.

[0056] The tool may be a handheld tool - which may also be referred to as a hand tool - a semi-stationary tool or a stationary tool.

[0057] In a preferred embodiment, the tool is a saw. It can be a hand saw, a semi-fixed saw or a fixed saw. An example of a hand saw is a circular hand saw. An example of a semi-fixed saw is a movable circular table saw. An example of a fixed saw is a panel saw.

[0058] The electrical energy storage unit can be a capacitor or a battery. It is irrelevant whether the electrical energy storage unit (ie capacitor or battery) is designed as a component of the actuator or as a component of the tool in terms of construction. It is only important that the electrical energy storage unit is electrically coupled to the actuating element.

[0059] The emergency brake unit is in particular an emergency brake unit which can be triggered multiple times.

[0060] The environmental parameter may comprise a detected or obtained ambient temperature. Thus, the actuator can always be operated with a high reliability level independently of the ambient temperature. At the same time, undesired aging phenomena can be avoided. This is due to the fact that, depending on the ambient temperature, a current level for actuating the actuating element can be selected which is sufficient to actuate the actuator reliably but also does not cause unnecessary thermal loading. In particular, in the case of relatively high ambient temperatures, a relatively low current level is selected. In the case of relatively low ambient temperatures, a relatively high current level is selected.

[0061] The first operating parameter may include the temperature of the actuating element. As already mentioned, the function of the actuating element is based on a thermally activated lattice transformation of the shape memory alloy. Thus, a reliable function of the actuating element may be ensured while avoiding excessive thermal loading of the shape memory alloy leading to undesirable aging effects.

[0062] Alternatively or additionally, the second operating parameter may include the rotation speed of the tool and / or the power consumption of the tool. Thus, triggering the emergency braking system by means of the actuator may only be allowed when the second operating parameter exceeds a defined rotation speed and / or a defined power consumption.

[0063] According to one embodiment, operating the actuator according to the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter comprises adjusting the actuating current parameter of the actuating element according to the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. It should also be understood that the actuator can only be operated according to the parameters that have been previously detected or obtained. In this regard, the actuating current parameter is understood to be a variable that characterizes the current used to actuate the actuating element. The actuating current parameter describes, for example, the maximum actuating current or the duration of the current supply. It is emphasized that due to the relatively short actuation time of only a few milliseconds, the actuating current parameter is adjusted at a certain time before actuation. The actuating current parameter has a direct impact on the aging of the actuating element.

[0064] In one variant, adjusting the actuation current parameter consists in adjusting the resistance applied between the energy storage unit and the actuation element according to the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. The process of adjusting the actuation current acting on the actuation element by means of the resistance.

[0065] In another variant, adjusting the actuation current parameter consists in adjusting the capacitance of the energy storage unit according to the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. The amount of charge that can be stored on the energy storage unit and can be delivered to the actuation element via the switching element is also adjusted. It should be understood that a relatively high amount of charge results in a relatively high and / or relatively persistent actuation current.

[0066] In this regard, creating an energy storage unit with adjustable capacitance consists in selecting an energy storage unit whose capacitance itself can be adjusted. Alternatively, an energy storage unit can be selected that includes two or more energy storage elements, each of which can be selectively switched on and off.

[0067] It is also possible that the adjustment of the actuation current parameter consists in adjusting the storage voltage of the energy storage unit as a function of the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. Via the storage voltage, the amount of charge that can be stored on the energy storage unit and that can be delivered to the actuation element via the switching element can also be adjusted. It should be understood that a relatively high amount of charge results in a relatively high and / or relatively persistent actuation current.

[0068] Alternatively or additionally, the adjustment of the actuation current parameter can be adjusted to adjust the actuation time of the switch element according to the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. Thus, the duration of the current delivery is adjusted according to the environmental parameter and / or the first operating parameter and / or the second operating parameter.

[0069] According to an exemplary embodiment, the actuating element is temperature controlled. This means that the temperature of the actuating element is adjusted to a specific value or a specific range of values. Preheating can also be considered for the case where the temperature is controlled so that the actuating element reaches a temperature above the ambient temperature. This can alternatively be called priming. Controlling the temperature of the actuating element ensures that it can be actuated independently of the ambient temperature. In particular, actuation independently of the ambient temperature requires constant energy. In other words, a first operating parameter of the actuating element describing the temperature of the actuating element is constant or remains within a predetermined range. This ensures that the actuating element functions in a reliable manner on the one hand and prevents aging processes on the other hand.

[0070] The temperature of the actuating element can be controlled in two ways. Heat is supplied to the actuating element from the outside, or an electric current is passed through the actuating element, which causes it to heat up. In both alternatives, the temperature of the actuating element can be precisely adjusted. Of course, these temperature control methods can also be combined.

[0071] The temperature of the actuating element can be controlled to be a temperature that is higher than the current ambient temperature and lower than the switching temperature of the actuating element (i.e., the temperature at which the lattice transition starts). For example, the temperature of the actuating element can be controlled to a temperature that corresponds to 50% to 90% of the switching temperature of the actuating element. In this way, it is ensured that the actuating element can be actuated starting from a temperature-controlled state with the aid of a relatively low actuating current and / or a relatively low amount of actuating charge. Due to the temperature control, a minimum temperature of the SMA wire is ensured, so that an actuating current that is less than the actuating current required at a lower temperature of the actuating element can be selected. This also helps to protect the actuating element from undesirable aging effects caused by excessive current and / or to ensure maximum performance over time that is independent of the ambient temperature.

[0072] In this respect, on the one hand, the temperature of the actuating element can be controlled to a specific temperature. On the other hand, the temperature-resistance characteristic curve of the shape memory alloy can be used to control the temperature of the actuating element to a temperature corresponding to the maximum resistance. The first case is referred to as temperature-dependent preheating or temperature control. The second case is referred to as resistance-dependent preheating or temperature control.

[0073] In a variant, the tool is deactivated until a desired minimum temperature of the actuating element is achieved. In this way, it is ensured that the emergency brake unit is ready for use before it can work with the tool.

[0074] Alternatively, as long as the desired minimum temperature of the actuating element has not yet been reached, a warning signal or warning indication may be output by means of a tool. In this way, a user who knows whether the emergency brake unit is ready for use may make a decision about whether he / she wishes to use the tool.

[0075] In another alternative, a sufficiently high actuation current and / or a sufficiently high actuation charge quantity is adjusted if the desired minimum temperature of the actuation element has not yet been reached. Once the desired minimum temperature is reached, the actuation current and / or the actuation charge quantity is reduced.

[0076] The above-mentioned purpose is also achieved by means of a control circuit for an actuator of an emergency brake unit of a motor-driven tool. The actuator comprises an actuating element, which comprises a shape memory alloy. The control circuit comprises at least one electrical energy storage unit and an electrical switching element. The electrical energy storage unit and the electrical switching element can be electrically coupled to the actuating element, so that the actuating element can be selectively supplied with electrical energy stored in the energy storage unit by actuation of the switching element. The energy storage unit has an adjustable capacitance and / or the control circuit has an adjustable resistance and / or the control circuit has an adjustable voltage converter electrically coupled to the energy storage unit, so that the storage voltage of the energy storage unit can be adjusted, and / or the actuation time of the electrical switching element can be adjusted. All these alternatives can be used to adjust the actuation current parameter. This can occur according to environmental parameters and / or first operating parameters and / or second operating parameters. As already mentioned, the actuation current parameter describes, for example, the duration of the maximum actuation current or current delivery. Therefore, by means of such a control circuit, the actuating element comprising a shape memory alloy can be controlled in the following manner: on the one hand, fast and reliable actuation is achieved, on the other hand, undesirable aging effects are prevented.

[0077] An adjustable voltage converter is, for example, a so-called boost converter.

[0078] The control circuit may also include a temperature control device, which may be coupled to the actuating element to control the temperature of the actuating element. With the aid of such a temperature control device, the effects and advantages already mentioned with respect to the method step of temperature control may be achieved. Reference is made to the above description.

[0079] The temperature control device may comprise a measuring instrument for measuring the temperature of the actuating element and / or for measuring the resistance of the actuating element. The resistance may be measured by a combined measurement of the current flowing through the actuating element and the voltage dropped across the actuating element. Thus, the temperature of the actuating element may be controlled by means of a closed loop system. Thus, a particularly precise temperature control is allowed.

[0080] If the temperature-resistance characteristic curve of the actuator element is known, temperature and resistance can be converted into one another.

[0081] In addition, the above-mentioned purpose is achieved by an actuator unit including a control circuit and an actuator according to the present invention. The actuator includes an actuating element, which includes a shape memory alloy. The actuator is electrically coupled to the control circuit. Therefore, the actuating element can be supplied with a current in a targeted manner, which current has a sufficient magnitude to achieve safe and reliable actuation of the actuator. In particular, sufficiently fast actuation of the actuator is achieved. However, at the same time, the current is relatively low so that excessive aging or even damage to the actuator is avoided. The low amount of current means a low thermal load of the shape memory alloy. This leads to relatively slow aging. Therefore, this actuator unit has a high level of reliability and a long service life. In particular, the actuator unit can be actuated multiple times.

[0082] The actuating element is preferably in the form of a wire. Since the actuating element comprises a shape memory alloy, when the wire is heated to a temperature above a triggering threshold, the wire shortens. Such a triggering threshold may also be referred to as a switching temperature. If the wire is subsequently cooled to the temperature of its environment, the shortening is reversed.

[0083] According to one variant, the actuating element is thermally insulated from its surroundings. Since the actuating element comprises a shape memory alloy, the shape memory alloy is also thermally insulated from its surroundings. Thus, temperature fluctuations of the shape memory alloy can be suppressed. This slows down undesirable aging of the shape memory alloy.

[0084] The above objects are also achieved by an emergency brake unit for a motor-driven tool, which comprises an actuator unit according to the invention. Such an emergency brake unit has a high level of reliability and a long service life. In particular, the emergency brake unit can be used multiple times, wherein the reliability can be maintained at a high level throughout the service life.

[0085] For the rest, the effects and advantages mentioned for any one aspect of the method according to the invention, the control circuit according to the invention, the actuator unit according to the invention and the emergency brake unit according to the invention may also be applied in an equivalent manner to all other aspects of the method according to the invention, the control circuit according to the invention, the actuator unit according to the invention and the emergency brake unit according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The invention will be explained below with the aid of various exemplary embodiments shown in the accompanying drawings. In the drawings:

[0087] Figure 1 A sawing device having an emergency brake unit is shown, which is equipped with an actuator unit, which comprises a control circuit according to the invention and an actuator which can be operated by means of the method,

[0088] Figure 2 Shows Figure 1 A sawing device, wherein the housing part and the protective cover are removed,

[0089] Figure 3 Shows Figure 2 A cross-sectional view of the sawing device along plane III,

[0090] Figure 4 An alternative embodiment of the emergency brake unit is shown corresponding to Figure 3 View,

[0091] Figure 5 The emergency brake unit is shown in a separate diagram along the Figure 2 The view in the direction V,

[0092] Figure 6 Another alternative embodiment of the emergency brake unit is shown corresponding to Figure 3 View,

[0093] Figure 7 Another alternative embodiment of the emergency brake unit is shown corresponding to Figure 3 View,

[0094] Figure 8 shows a view of an emergency brake unit according to another embodiment,

[0095] Fig. 9 Shows Figure 8 A cross-sectional view of the emergency brake unit along plane IX-IX,

[0096] Fig.10 The circuit diagram shows Figure 1 and Figure 2 of an actuator unit according to the invention, wherein the actuator is represented by an actuating element in the form of a wire made of a shape memory alloy,

[0097] Fig.11 Corresponding to Figure 6 The diagram of FIG. 1 shows an alternative embodiment of an actuator unit according to the invention,

[0098] Fig.12 Based on Figure 6 and Figure 7 The diagram of FIG. 1 shows another alternative embodiment of the actuator unit according to the invention, and

[0099] Fig.13 Based on Figures 6 to 8 The illustration of shows a further alternative embodiment of the actuator unit according to the invention. DETAILED DESCRIPTION

[0100] Figure 1 and Figure 2 A motor-driven tool 8 is shown, which in the example shown is a sawing device 10 , more precisely a miter saw.

[0101] The sawing device 10 comprises a base part 12 comprising a support surface 14 for a workpiece 16. The workpiece 16 is to be understood as an example.

[0102] Furthermore, the sawing device 10 comprises a pivot device 18 which is mounted in an articulated manner on a first portion 18a on the base portion 12. A disc-shaped saw blade 20 is mounted on a second portion 18b spaced apart from the first portion 18a. Furthermore, a handle 22 is provided on the second portion 18b.

[0103] Thus, by means of the handle 22 , a user of the sawing device 10 can cause the rotating saw blade 20 to interact with a workpiece 16 mounted on the support surface 14 to saw the workpiece.

[0104] The sawing device 10 , ie the motor-driven tool 8 , is also equipped with an emergency brake unit 24 .

[0105] The emergency brake unit 24 is designed to brake the saw blade 20 until the saw blade 20 stops when it is detected that the user has come into contact with the saw blade 20 or there is a risk of such contact while the saw blade 20 is rotating.

[0106] In this respect, the saw blade 20 acts as a capacitive sensor element, ie, the capacitance of the saw blade 20 is continuously detected. For situations where the capacitance is outside a predetermined normal range, contact is detected.

[0107] Figures 3 to 9 Different embodiments of the emergency brake unit 24 are shown.

[0108] In this regard, the emergency brake unit 24 includes a brake caliper 26 engaged over the edge of the saw blade 20, whereby a pressure element 28 provided on the brake caliper 26 is arranged on a first axial side of the saw blade 20, and a brake cam 30 rotatably mounted on the brake caliper 26 is arranged on a second axial side of the saw blade 20.

[0109] In a more general manner, the brake cam 30 may also be referred to as a brake element 29 .

[0110] The brake cam 30 is coupled to an actuator unit 32, which includes an actuator 31 and a control circuit, which will be described below and is electrically coupled to the actuator. By means of the actuator 31, the brake cam 30 can be selectively rotated so that it presses the saw blade 20 against the pressure element 28 and thus brakes the saw blade until it stops.

[0111] exist Figure 3In a variation of , the actuator 31 comprises an actuating element 34, which comprises a shape memory alloy 36. Specifically, the actuating element 34 is formed as a wire made of the shape memory alloy 36.

[0112] The actuating element 34 is fastened to a fastening element receiver at a first end 34a. The fastening element receiver may be part of the brake caliper 26 or part of a retaining structure 35 fixed to the brake caliper 26. The retaining structure 35 may be formed by an actuator housing 39 fastened to the brake caliper 26.

[0113] Of course, the holding structure 35 may also be formed by the brake caliper 26 , or by the brake caliper 26 and the actuator housing 39 together.

[0114] The other end 34b of the actuating element 34 is fastened to a slide 38 which is mounted so as to be displaceable in translation relative to the brake caliper 26. The slide 38 is spring-loaded in a direction corresponding to the tensile loading of the actuating element 34. Furthermore, the slide 38 is coupled to the brake cam 30 via an actuating pin 40 or can be coupled to the brake cam 30 via an actuating pin 40.

[0115] If the actuator element 34 is powered with a current of sufficient magnitude, a thermally induced lattice transformation of the shape memory alloy 36 occurs, which causes the actuator element 34 to shorten. This causes the slider 38 and the actuator pin 40 to move toward Figure 3 As a result, the brake cam 30 engages with the saw blade 20 and brakes it until it stops.

[0116] To improve understanding, Figure 3 In the figure, the actuating pin 40 and the braking cam 30 are shown in a non-actuated state with solid lines. The non-actuated state relates to a state in which the actuating element 34 has not been powered with a sufficient current. Therefore, the braking cam 30 does not interact with the saw blade 20. In addition, the actuating pin 40 and the braking cam 30 are shown in an actuated state with dashed lines. In this state, the actuating element 34 has been powered with a sufficient current, so that in Figure 3 , the actuating pin 40 has been displaced to the right and the brake cam 30 has been rotated in the clockwise direction. The saw blade 20 is therefore clamped between the brake cam 30 and the pressure element 28. In the actuated state, the actuating pin 40 and the brake cam 30 are separated from each other, ie spaced apart.

[0117] Figure 4 An alternative embodiment of an actuator unit 32 is shown. In this embodiment, the first end 34a of the actuating element 34 is fixed relative to the brake caliper 26 as usual.

[0118] and Figure 3Compared to the variant of , the second end 34b is fastened to the brake cam 30. The brake cam 30 is spring loaded. The loading direction again corresponds to the tensile loading direction of the actuating element 34.

[0119] exist Figure 4 In a variation of , if the actuating element 34 is powered with a current of sufficient magnitude, a thermally induced lattice transformation of the shape memory alloy 36 occurs, which causes the actuating element 34 to shorten. This causes the brake cam 30 to rotate, so that it engages with the saw blade 20 and brakes it until it stops. Figure 4 In the embodiment of the present invention, when the emergency brake unit 24 is triggered, the brake cam 30 rotates in the clockwise direction.

[0120] Therefore, the actuator 31 for operating the emergency brake unit 24 includes an actuating element 34 (the actuating element 34 includes a shape memory alloy 36), a retaining structure 35 and a spring element 37 arranged on the retaining structure 35, wherein the spring element 37 biases the second end 34b of the actuating element 34 relative to the first end 34a of the actuating element 34 and / or defines a preferred position of the actuating pin 40—preferably extending along the pin axis 40a relative to the retaining structure 35.

[0121] The actuating element 34 always extends along a shortening direction extending from a first end 34 a of the actuating element 34 to a second end 34 b of the actuating element 34 .

[0122] exist Figure 3 In the variant shown, the actuating pin 40 is mounted so as to be displaceable in translation relative to the retaining structure along a pin axis 40 a. The actuating pin 40 is mounted in a through hole on the retaining structure 35 .

[0123] The actuating element 34 is fastened at its first end 34 a to a fastening element receiver of the holding structure 35 and is or can be coupled to the braking cam 30 at its second end 34 b .

[0124] exist Figure 3 In the variant shown, the second end 34 b is or can be coupled to the brake cam 30 via an actuating pin 40 .

[0125] The pin axis 40 a and the shortening direction of the actuating element 34 preferably extend in parallel.

[0126] Alternatively or additionally, the actuating pin 40 and the second end 34 b of the actuating element 34 may be displaced parallel to each other in the same direction by triggering the emergency brake unit 24 .

[0127] Preferably, the movement is a linear movement.

[0128] exist Figure 3In the variant shown, the actuating pin 40 and the second end 34 b of the actuating element 34 are coupled by means of a slide 38 , so that the actuating pin 40 can engage with the brake cam 30 via the slide 38 .

[0129] The slide 38 engages with a guide contour arranged on the holding structure 35. In this way, a rotation of the slide 38 relative to the holding structure can be avoided. Alternatively, provision can also be made for the actuating pin 40 to engage with a guide contour arranged on the holding structure.

[0130] exist Figure 4 In the variant shown, the second end 34 b of the actuating element 34 engages directly with the brake cam 30 .

[0131] The first end 34a and the second end 34b of the actuating element 34 are received, for example, in sleeves 84a, 84b. The sleeves 84a, 84b can be pressed or crimped onto the actuating element 34, i.e. onto the wire consisting of the shape memory alloy 36. Thus, the wire can be coupled in a simple manner at its first end 34a to the retaining structure and at its second end 34b to the slide 38 or the brake cam 30.

[0132] Alternatively, the first end 34a and the second end 34b of the actuating element 34 can also be extrusion coated with an electrically insulating synthetic material, for example, to form sleeves 84a, 84b. In other words, according to this alternative, sleeves 84a, 84b are injection molded on the first end 34a or second end 34b respectively associated.

[0133] However, the second end 34 b can also be extrusion-coated with the slide 38 and / or embedded in the slide 38 .

[0134] Alternatively or additionally, the first end 36a can be extrusion-coated with the holding structure and / or embedded in the holding structure.

[0135] The first end 34a and the second end 34b of the actuating element 34 preferably form electrical terminals of the actuating element 34. For example, a cable is directly soldered, crimped or plugged onto the first end 34a and the second end 34b by means of plug contacts.

[0136] exist Figure 6 In a variation of , the actuator 31 also includes an actuating element 34, which includes a shape memory alloy 36. Specifically, as described above, the actuating element 34 is formed as a wire made of the shape memory alloy 36.

[0137] The actuating element 34 is fastened at a first end 34 a to a fastening element receptacle of a holding structure 35 which, in the example shown, is formed by an actuator housing 39 .

[0138] The other end 34 b of the actuating element 34 is fastened to a slide 38 which is mounted so as to be displaceable on the retaining structure 35 , ie on the actuator housing 39 , via two elastic bearing elements 74 which in the present case are each designed as a leaf spring element.

[0139] As already explained, the two ends 34a, 34b of the actuating element 34 are provided with injection-molded sleeves 84a, 84b.

[0140] In this respect, the slide 38 is substantially L-shaped, wherein the relatively longer branch of the L-shaped slide 38 is oriented parallel to the actuating element 34 .

[0141] Two elastic supporting elements 74 are connected to the relatively long branches.

[0142] The relatively shorter branch of the L-shaped slide 38 is oriented substantially at right angles to the relatively longer branch.

[0143] An actuating pin 40 with a pin axis 40a, more precisely, the actuating element-side end of the actuating pin 40, is rigidly connected to the relatively short branch. The actuating pin 40 points away from the relatively long branch and extends through a through opening provided on the retaining structure 35, i.e. on the actuator housing 39, so that the free end of the actuating pin 40 is located in the vicinity of the brake element 29, which in the present case is in the form of a brake cam 30. Thus, the brake element-side end 41 of the actuating pin 40 can be located on the brake element 29, i.e. on the brake cam 30, or can be placed on the brake element 29, i.e. on the brake cam 30, when the actuating element 34 is actuated.

[0144] Therefore, there is no tensile coupling between the actuating pin 40 and the brake element 29, ie the brake cam 30. This means that no tensile forces can be introduced into the brake element 29 by means of the actuating pin. Incidentally, this also applies to Figure 3 implementation method.

[0145] The free end of the actuating pin 40 (ie, the brake element-side end 41 of the actuating pin 40 ) is rounded.

[0146] The through-opening through which the actuating pin 40 extends serves to guide the actuating pin 40 .

[0147] Furthermore, a retaining ring is fastened in the region of the brake element-side end 41 of the actuating pin 40 , by means of which the movement of the brake element-side end 41 of the actuating pin 40 in the direction of the retaining structure 35 , ie in the direction of the actuator housing 39 , is limited.

[0148] The center axis of the actuating pin 40 (ie, the pin axis 40 a ) extends in a parallel offset manner relative to the actuating element 34 .

[0149] If the actuator element 34 is powered with a current of sufficient magnitude, a thermally induced lattice transformation of the shape memory alloy 36 occurs, which causes the actuator element 34 to shorten. This causes the slider 38 and the actuator pin 40 to move toward Figure 6 As a result, the brake cam 30 engages with the saw blade 20 and brakes it until it stops.

[0150] This movement of the slide 38 is limited due to the relatively short branches of the slide 38 which may be located on the retaining structure 35 , ie on the actuator housing 39 .

[0151] Assuming that the actuating element 34 is no longer supplied with current and thus cools down, the previous thermally induced lattice transformation is reversed and the actuating element 34 elongates back to its original length.

[0152] The slide 38 is always spring-loaded by the elastic bearing element 74 in a direction corresponding to the tensile loading of the actuating element 34. In this way, the slide 38 is reliably returned to its starting position.

[0153] In short, according to Figure 6 In the embodiment of , the second end 34 b of the actuating element 34 is drivingly coupled to the brake element 29 , ie the brake cam 30 , via a slide 38 and an actuating pin 40 .

[0154] In terms of compact design, the brake element-side end 41 of the actuating pin 40 is arranged between the first end 34a of the actuating element 34 and the second end 34b of the actuating element 34 in a direction parallel to the actuating element 34. If a line perpendicular to the actuating element 34 is imaginarily drawn at each end 34a, 34b, this can be seen from Figure 6 It can be seen immediately from the view of that the line intersects the pin axis 40a. The brake element-side end 41 of the actuating pin 40 is then located between these two intersection points.

[0155] In addition, according to Figure 6 In the embodiment, the length L of the actuating element 34 BE is smaller than the length L of the emergency brake unit 24 and the actuating element 34 BE The dimension A in the parallel direction. In addition, the length L of the actuator BE completely located with the length L of the actuating element 34 BE Dimension A of the emergency brake unit 24 measured parallel to the actuating element. Dimension A (also referred to as the maximum dimension) is formed by the dimension of the brake caliper 26 measured parallel to the actuating element. Figure 6 It can be seen directly that the actuating element 34 is shorter than this dimension A. Figure 6If vertical lines are drawn from top to bottom at the beginning and end of dimension A of the brake caliper 26 , the actuating element 34 is located between these lines.

[0156] Figure 7 Shown with Figure 6 Therefore, the following will only explain the embodiment with respect to Figure 6 For the rest, please refer to the Figure 6 explanations of the implementation methods.

[0157] according to Figure 7 Implementation and basis of Figure 6 A first difference between the embodiments of is that the slide 38 is mounted so as to be movable on the holding structure 35 , ie on the actuator housing 39 , by means of two articulated arms 76 .

[0158] The articulated arms 76 are rigid in nature. However, they are connected in each case to the slide 38 via a first pivot joint and in each case to the holding structure 35 via a second pivot joint.

[0159] The second difference is that now again a spring element 37 is provided. The spring element 37 is arranged between a relatively short branch of the L-shaped slide 38 and the part of the retaining structure 35, ie the actuator housing 39, opposite to this branch.

[0160] Therefore, the slide 38 is always spring-loaded by the spring element 37 in a direction corresponding to the tensile loading of the actuating element 34. In this way, the slide 38 reliably returns to its starting position if the actuating element 34 is no longer supplied with current.

[0161] Furthermore, a spring element 37 designed as a helical spring circumferentially surrounds the actuating pin 40 .

[0162] The spring element 37 and the actuating pin 40 are also arranged coaxially.

[0163] Another embodiment of the emergency brake unit 24 is Figure 8 and Fig. 9 Shown in. Figure 8 In particular, the brake caliper 26 of the emergency brake unit 24 is shown in a view in the direction lying in the saw blade plane of the saw blade 20. The position of the saw blade 20 is indicated by a dashed line.

[0164] Fig. 9 The relevant cross-section in plane IX-IX is shown.

[0165] In accordance with Figure 8 and Fig. 9In the embodiment of , the actuating element 34 and the slide 38 , to which the second end 34 b of the actuating element 34 is fastened, are arranged on a common carrier plate 78 , which is designed as a plate, for example.

[0166] The control circuit 42, which will be explained in further detail below, is also disposed on the carrier board 78. The carrier board 78 with the control circuit 42 may be referred to as a control unit.

[0167] As previously mentioned, the brake cam 30 may be actuated by means of an actuation pin 40 rigidly attached to the slider 38 .

[0168] The carrier plate 78 and the actuating element 34 are positioned so that they mechanically shield the drive coupling portion of the brake element 29, ie the area of ​​the brake cam 30 formed to allow the actuating pin 40 to be located thereon. Fig. 9 can be seen in the view.

[0169] In this view, a human finger or a human hand cannot reach the drive coupling part from above, since access is blocked via the carrier plate 78 and the actuating element 34. This also applies to foreign bodies, such as dust particles.

[0170] If already combined Figure 6 The implementation method explained in accordance with Figure 8 and Fig. 9 In the embodiment, the length L of the actuating element 34 BE is smaller than the length L of the emergency brake unit 24 between the actuating element 34 BE The dimension A in the parallel direction. In addition, the length L of the actuator element 34 BE completely located with the length L of the actuating element 34 BE Within dimension A of the emergency brake unit 24 measured in parallel.

[0171] In all the previously explained variants, the slide 38 and the actuating pin 40 may be more generally referred to as an intermediate element 80 .

[0172] Another term for the actuating pin 40 is a push rod.

[0173] Furthermore, in the previously described example, the combination of the actuator 31 and the brake element 29 (i.e., the brake cam 30) may be referred to as an emergency brake assembly 82. The emergency brake assembly 82 thus represents a subunit of the emergency brake unit 24, wherein, as already explained, the emergency brake unit 24 is formed to brake the saw blade 20 until the saw blade 20 stops.

[0174] Fig.10 An embodiment of the actuator unit 32 is shown in the form of a circuit diagram.

[0175] The actuating element 34 of the actuator 31 is composed of a variable resistor R BE express.

[0176] The actuator 31 (ie the actuating element 34 ) is electrically connected to a control circuit 42 , which is formed to selectively supply electrical energy to the actuating element 34 , thus causing the above-mentioned microstructural conversion.

[0177] In this respect, the control circuit 42 comprises an electrical energy storage unit 44 in the form of a capacitor having an adjustable capacitance.

[0178] Furthermore, the control circuit 42 has an electrical switching element 45, by means of which the energy storage unit 44 and the actuating element 34 can be selectively electrically coupled. The electrical coupling takes place via a resistor 46 which is optionally provided.

[0179] The control circuit 42 further comprises a charging circuit 48 for the energy storage unit 44. The charging circuit has a DC voltage source 50, which is coupled to the energy storage unit 44 via an adjustable voltage converter 52 and a further electrical switching element 54. The resistance of the charging circuit 48 is represented by a resistor R LS express.

[0180] The electrical switching element 45 and also the further electrical switching element 54 are actuated by means of a trigger control unit 56 serving as a sensor element, which is coupled to the saw blade 20 .

[0181] The electrical switching element 45 is open in the initial state, ie the actuating element 34 is electrically disconnected from the energy storage unit 44. The further switching element 54 is closed, so that the energy storage unit 44 is brought to or maintained in the desired charge state by means of the DC voltage source 50.

[0182] When the trigger control unit 56 detects actual contact or a risk of contact between the user and the saw blade 20, the electrical switch element 45 is closed and the further electrical switch element 54 is opened. Thus, the energy storage unit 44 is electrically connected to the actuating element 34, so that an electric current is delivered through the actuating element 34, which current causes a microstructural transformation of the shape memory alloy 36.

[0183] exist Fig.10 In the exemplary embodiment, this can occur according to the first operating parameter B1 of the actuator 31. In the exemplary embodiment shown, this parameter is resistance or temperature. Since the actuating element 34 has a temperature-dependent characteristic resistance, resistance and temperature can be converted into each other. The resistance curve of the actuating element 34 over temperature can be assumed to be known in advance.

[0184] To this end, the control circuit 42 comprises a circuit for measuring the current I flowing through the actuating element 34 BE The current measuring unit 58 measures the voltage U dropped across the actuating element.BE The voltage measuring unit 60 is provided.

[0185] The current measuring unit 58 and the voltage measuring unit 60 are coupled to the state control unit 62 via signal technology. The resistance of the actuating element 34 can be determined by the state control unit 62 using the voltage U BE and current I BE The temperature of the actuating element 34 can also be determined via the known correlation between resistance and temperature.

[0186] The state control unit 62 is also coupled to the voltage converter 52 via signal technology. Thus, the voltage can be adjusted depending on the resistance or temperature of the actuating element 34, which is distributed between the adjustable resistor 46 and the energy storage unit 44. In other words, the storage voltage of the energy storage unit 44 can be adjusted.

[0187] It will be appreciated that a current must flow through the actuation element 34 in order for its resistance and / or its temperature to be determined by means of the current measuring unit 58 and the voltage measuring unit 60. This means that the resistance and / or the temperature can be measured during actuation of the actuation element 34.

[0188] Alternatively or additionally, a measuring method can be carried out by means of the trigger control unit 56 , in which the actuating element 34 is only temporarily supplied with current in order to measure the resistance and / or the temperature.

[0189] The state control unit 62 is also coupled to an environmental sensor 63a via signal technology, by which an environmental parameter U can be detected. In the example shown, the environmental parameter U is the ambient temperature. Therefore, the voltage converter 52 and / or the energy storage unit 44 can also be operated and / or adjusted according to the ambient temperature.

[0190] In addition, the state control unit 62 is coupled to a tool state sensor 63b via signal technology. The tool state sensor is configured to determine a second operating parameter B2 of the tool 8 equipped with the actuator 31. In the present example, the tool state sensor is a rotation speed sensor that measures the rotation speed of the tool 8. Therefore, the voltage converter 52 and / or the energy storage unit 44 can also be operated and / or adjusted according to the rotation speed.

[0191] Fig.11 An alternative embodiment of the actuator unit 32 is shown in the form of a circuit diagram. Fig.10 Identical or mutually corresponding elements are denoted by the same reference numerals.

[0192] First, according to Fig.11 In an embodiment of , the energy storage unit 44 can no longer be adjusted but has a constant storage capacitance.

[0193] However, resistor 46 is optional.

[0194] Furthermore, a heating circuit or temperature control device 64 is provided.

[0195] In this respect, the electrical switch element 45 is modified such that, as previously described, in a first position it connects the energy storage unit 44 to the actuating element 34 in an electrically conductive manner.

[0196] In the second position, the electrical switching element 45 connects the actuating element 34 to the heating circuit or the temperature control device 64 , so that a heating current can be conveyed through the actuating element 34 in order to heat it to a desired temperature.

[0197] In accordance with Fig.11 In the embodiment of the present invention, the state control unit 62 also includes a heating regulator 66.

[0198] The heating controller 66 uses the current I determined by means of the current measuring unit 58 BE and the voltage U determined by means of the voltage measuring unit 60 BE as an input parameter.

[0199] The current measuring unit 58 and the voltage measuring unit 60 thus form a measuring instrument of the temperature control device 64 , by means of which the temperature of the actuating element 34 and / or the electrical resistance of the actuating element 34 can be measured.

[0200] As already mentioned, the resistance of the actuation element 34 can be calculated therefrom, or the temperature of the actuation element 34 can be calculated using the known correlation between temperature and resistance.

[0201] Thus, the heating regulator 66 can be operated with temperature as reference variable or with resistance as reference variable.

[0202] In this respect, the additional electrical switching element 68 can be controlled by means of the heating controller 66 , for example, using a pulse width modulated signal.

[0203] The voltage converter 52 is regulated as usual.

[0204] Fig.12 Another alternative embodiment of the actuator unit 32 is shown in the form of a circuit diagram. Fig.10 and Fig.11 The same or mutually corresponding elements are denoted by the same reference numerals.

[0205] According to Fig.11 Compared with the implementation method according to Fig.12In the embodiment of , the voltage converter 52 is no longer adjustable. This means that the voltage converter 52 always sets the voltage of the energy storage unit 44 (which in the present case is formed by the energy storage elements 44a, 44b) to a fixed value.

[0206] The energy storage unit 44 therefore now comprises two energy storage elements 44a, 44b, which are each formed as a capacitor.

[0207] The energy storage elements are electrically connected in parallel.

[0208] Furthermore, instead of only one optional resistor 46 , two optional resistors 46 a , 46 b are now provided, which are each connected in parallel with one another and in series with one of the energy storage elements 44 a , 44 b .

[0209] The energy storage element 44 a and the resistor 46 a may be coupled to a DC voltage source 50 via an electrical switching element 54 as usual.

[0210] The energy storage element 44 b and the resistor 46 b can be selectively coupled by means of an additional electrical switch element 70 , ie the energy storage element 44 b and the resistor 46 b are connected to the DC voltage source 50 only when the electrical switch element 54 and the electrical switch element 70 are closed.

[0211] The electrical switching element 70 is connected by means of the state control unit 62 .

[0212] Thus, the energy storage element 44 b and the resistor 46 b may be utilized depending on the resistance and / or temperature of the actuation element 34 .

[0213] Furthermore, the energy storage element 44b and the resistor 46b may be utilized depending on the environmental parameter U determined by means of the environmental sensor 63a and / or depending on the second operating parameter B2 determined by means of the machine state sensor 63b.

[0214] Fig.13 An additional alternative embodiment of an actuator unit 32 is shown in the form of a circuit diagram. Only the differences with respect to the preceding embodiment will be discussed below. Identical or mutually corresponding elements are denoted by the same reference numerals.

[0215] According to Fig.11 Compared with the implementation method according to Fig.13 In the embodiment of , the voltage converter 52 is no longer adjustable. This means that the voltage converter 52 always sets the voltage of the energy storage unit 44 to a fixed value.

[0216] Another difference is that an adjustable resistor 72 is provided in series with the resistor 46. The adjustable resistor is adjusted by means of the state control unit 62.

[0217] As previously described, this can be achieved based on the environmental parameter U determined with the aid of the environmental sensor 63a and / or based on the resistance determined with the aid of the current measuring unit 58 and the voltage measuring unit 60 and / or based on the temperature determined with the aid of the current measuring unit 58 and the voltage measuring unit 60 and / or based on the second operating parameter B2 determined with the aid of the machine state sensor 63b.

[0218] In short, according to Fig.10 and Fig.12 An embodiment of the invention is characterized by an energy storage unit 44 having an adjustable capacitance.

[0219] according to Fig.12 and Fig.13 The control circuit 42 also has adjustable resistors 46 , 46 a , 46 b , 72 .

[0220] In addition, according to Fig.10 and Fig.13 In the case of the control circuit 42 , the voltage converter 52 is adjustable, so that the storage voltage of the energy storage unit 44 can be adjusted.

[0221] In all control circuits 42 , the actuation time of the electrical switching element 45 is also adjustable.

[0222] In all of the aforementioned embodiments, the actuator 31 can be operated by means of a method for operating an actuator of an emergency brake unit.

[0223] An ambient parameter U, in this case the ambient temperature, is detected by means of the ambient sensor 63 a.

[0224] Furthermore, in all the aforementioned embodiments, the resistance and / or the temperature of the actuating element 34 is detected by means of the current measuring unit 58 and the voltage measuring unit 60. In brief, these may be referred to as first operating parameters B1 of the actuator 31 .

[0225] In all embodiments, provision is also made for detecting a second operating parameter B2 of the tool 8 equipped with the actuator 31 (in this case the rotational speed) by means of the machine state sensor 63b.

[0226] Based on this, in all embodiments, the actuator 31 operates according to the environmental parameter U, the first operating parameter B1 and the second operating parameter B2. This means that the actuation current parameter SP of the actuation element 34 is adjusted according to the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0227] In accordance with Fig.12 and Fig.13In this respect, in an embodiment of the present invention, the resistance applied between the energy storage unit 44 and the actuation element 34 is adjusted as a function of the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0228] In accordance with Fig.10 and Fig.12 In an embodiment, for this purpose, the capacitance of the energy storage unit 44 is adjusted as a function of the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0229] In addition, according to Fig.10 and Fig.11 In the embodiment, the storage voltage of the energy storage unit 44 is adjusted via the adjustable voltage converter 52 according to the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0230] Furthermore, in all embodiments, adjusting the actuation current parameter SP consists in adjusting the actuation time of the switching element 54 as a function of the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0231] In addition, according to Fig.11 , Fig.12 and Fig.13 In the embodiment of the present invention, the temperature of the actuating element 34 can be controlled by means of the temperature control device 64 to a temperature which is higher than the current ambient temperature and lower than the switching temperature of the actuating element 34 .

[0232] In the present case, it is explained that the actuation current parameter SP is adjusted as a function of the environmental parameter U, the first operating parameter B1 and the second operating parameter B2. However, it should be understood that it is also possible to use only one or two of these parameters.

[0233] In all of the foregoing exemplary embodiments, the emergency brake unit 24 or the emergency brake assembly 82 may operate as follows.

[0234] In a first step, the brake element 29 (in the present case the brake cam 30) is moved by means of the actuating element 34. In this respect, the actuating element 34 is shortened by a corresponding current supply. Figure 3 and Figures 6 to 9 In the embodiment of the invention, a compressive force is applied to the brake cam 30 via the actuating pin 40. Figure 4 In the embodiment of FIG. 5 , the second end portion 34 b of the actuating element 34 is directly fastened to the brake cam 30 and applies a tensile force thereto.

[0235] Thus, in all embodiments, the brake cam 30 is in contact with the saw blade 20. In the present case, since the emergency brake assembly 82 or the emergency brake unit 24 is designed in a self-reinforcing manner, the brake cam 30 is dragged by the saw blade 20 due to the contact. This results in the brake cam 30 pressing the saw blade 20 against the pressure element 28 with increasing force until the saw blade 20 stops.

[0236] In this respect, after the initial movement of the brake cam 30, the movement coupling between the actuating element 34 and the brake element 29 (ie the brake cam 30) is terminated or cancelled. Figure 3 and Figures 6 to 9 In the embodiment of , this occurs because the brake element-side end 41 of the actuating pin 40 is lifted off the brake element 29 (ie, from the brake cam 30). Figure 4 In the embodiment of , this occurs due to the fact that the brake cam 30 is moved far enough that the actuating element 34 is no longer under mechanical stress and thus tensile forces can no longer be introduced into the brake element 29 , ie the brake cam 30 .

[0237] As a result, the actuating element 34 can return to its initial position, i.e. to its unactuated position, after appropriate cooling. For this purpose, the thermally induced microstructural transformation is reversed. The return occurs independently of the brake element 29 (i.e. the brake cam 30), which can be returned separately from the actuating element 34.

[0238] The foregoing description relates to a sawing device 10 in the form of a miter saw. However, it should be understood that the design as a miter saw is merely one example and the foregoing description also applies to other types of sawing devices, such as a band saw.

[0239] Reference numerals list

[0240] 8 Motor Driven Tools

[0241] 10 Sawing device

[0242] 12 Base part

[0243] 14 Support surface

[0244] 16 Workpiece

[0245] 18 Pivot device

[0246] 18a Part 1

[0247] 18b Part 2

[0248] 20 Saw Blade

[0249] 22 Handle

[0250] 24 Emergency brake unit

[0251] 26 Brake caliper

[0252] 28 Pressure element

[0253] 29 Braking element

[0254] 30 Brake cam

[0255] 31 Actuator

[0256] 32 Actuator unit

[0257] 34 Actuating element

[0258] 34a First end

[0259] 34b Second end

[0260] 35. Maintain structure

[0261] 36 Shape memory alloy

[0262] 37 Spring element

[0263] 38 Slide

[0264] 39 Actuator housing

[0265] 40 Actuating pin

[0266] 40a Pin axis

[0267] 41 brake element side end of the actuating pin

[0268] 42 Control Circuit

[0269] 44 Energy storage unit

[0270] 44a Energy storage element

[0271] 44b Energy storage element

[0272] 45 Electrical switch element

[0273] 46 Resistors

[0274] 46a Resistor

[0275] 46b Resistor

[0276] 48 Charging Circuit

[0277] 50 DC voltage source

[0278] 52 Voltage Converter

[0279] 54 Other electrical switching elements

[0280] 56 Trigger control unit

[0281] 58 Current measurement unit

[0282] 60 Voltage measurement unit

[0283] 62 Status control unit

[0284] 63a Environmental Sensor

[0285] 63b Machine Status Sensor

[0286] 64 Heating circuit, temperature control device

[0287] 66 Heating Regulator

[0288] 68 Electrical switch element

[0289] 70 Electrical switch element

[0290] 72 Resistors

[0291] 74 elastic support element

[0292] 76 Articulated Arm

[0293] 78 Loading plate

[0294] 80 Intermediate components

[0295] 82 Emergency brake assembly

[0296] 84a First sleeve

[0297] 84b Second sleeve

[0298] A Size

[0299] B1 First operating parameter

[0300] B2 Second operating parameter

[0301] I BE The current through the actuator

[0302] L BE Length of the actuator

[0303] R BE Resistance of the actuator

[0304] R LS Charging circuit resistance

[0305] SP actuation current parameters

[0306] UEnvironmental parameters

[0307] U BEThe voltage drop across the actuator

Claims

1. An emergency brake assembly (82) for a motor-driven tool (8), comprising: Structure (35); A brake element (29), in particular a brake cam (30) or a pressure piece, is movably mounted on the holding structure (35); and a linear actuating element (34) comprising a shape memory alloy (36), wherein a first end (34a) of the actuating element (34) is fastened to the holding structure (35) and a second end (34b) of the actuating element (34) is drivingly coupled to the brake element (29).

2. The emergency brake assembly (82) according to claim 1, wherein the second end (34b) of the actuating element (34) is fastened to the brake element (29).

3. The emergency brake assembly (82) according to claim 1, wherein the second end (34b) of the actuating element (34) is coupled to the brake element (29) via at least one intermediate element (80).

4. The emergency brake assembly (82) according to claim 3, wherein the at least one intermediate element (80) comprises a slide (38) which is movably mounted on the holding structure (35).

5. Emergency brake assembly (82) according to claim 4, wherein the slide (38) is mounted on the holding structure (35) in such a way that it can be moved in translation via a sliding guide.

6. Emergency brake assembly (82) according to claim 4 or 5, wherein the slide is mounted on the holding structure (35) in a movable manner via at least one articulated arm (76).

7. Emergency brake assembly (82) according to any one of claims 4 to 6, wherein the slide (38) is connected to the retaining structure (35) via an elastic bearing element (74).

8. An emergency brake assembly (82) according to any one of claims 3 to 7, wherein the at least one intermediate element (80) includes a push rod or an actuating pin (40) having a brake element side end (41), wherein the brake element side end (41) of the push rod or the actuating pin (40) is located on the brake element (29) or can be placed on the brake element (29).

9. The emergency brake assembly (82) according to claim 8, wherein the brake element-side end (41) of the push rod or actuating pin (40) is separated from the brake element (29) via a tensile force or can be separated from the brake element (29) via a tensile force.

10. An emergency brake assembly (82) according to claim 8 or 9, wherein in a direction parallel to the actuating element (34), the brake element side end (41) of the push rod or actuating pin (40) is located between the first end (34a) of the actuating element (34) and the second end (34b) of the actuating element (34).

11. The emergency brake assembly (82) according to any one of claims 8 to 10, wherein the push rod or actuating pin (40) has a central axis (40a), and the central axis (40a) extends parallel to the actuating element (34).

12. The emergency brake assembly (82) of claim 11, wherein the central axis (40a) of the push rod or actuating pin (40) is spaced apart from the actuating element (34).

13. Emergency brake assembly (82) according to any one of claims 8 to 12, wherein the push rod or actuating pin (40) is guided on the retaining structure (35).

14. Emergency brake assembly (82) according to any one of claims 8 to 13, wherein the brake element-side end (41) of the actuating pin (40) or push rod is rounded.

15. Emergency brake assembly (82) according to any one of claims 8 to 14 and any one of claims 3 to 7, wherein the actuating element-side end of the push rod or actuating pin (40) is coupled to the slide (38).

16. Emergency brake assembly (82) according to any one of the preceding claims, wherein the actuating element (34) is guided by means of a guide element.

17. The emergency brake assembly (82) according to any of the preceding claims, further comprising a spring element (37), by means of which the actuating element (34) is directly or indirectly spring-loaded in a direction corresponding to the tensile loading of the actuating element (34).

18. The emergency brake assembly (82) of claim 17, wherein the spring element (37) at least partially circumferentially surrounds the push rod or actuating pin (40), And / or wherein the spring element (37) and the push rod or actuating pin (40) are coaxially arranged.

19. The emergency brake assembly (82) according to claim 17 or 18, wherein the spring element (37) at least partially circumferentially surrounds the actuating element (34).

20. The emergency brake assembly (82) according to any one of the preceding claims, wherein the retaining structure (35) is formed by the actuator housing (39) and / or the brake caliper (26).

21. The emergency brake assembly (82) according to claim 20, wherein a control unit for the actuating element (34) is at least partially integrated into the actuator housing (39).

22. An emergency brake assembly (82) according to any of the preceding claims, wherein a first sleeve (84a) is arranged on the first end (34a) of the actuating element (34), and the first end (34a) of the actuating element (34) is fastened to the retaining structure (35) via the first sleeve (84a).

23. An emergency brake assembly (82) according to any of the preceding claims, wherein a second sleeve (84b) is arranged on the second end (34b) of the actuating element (34), and the second end (34b) of the actuating element (34) is drivingly coupled to the brake element (29) via the second sleeve (84b).

24. The emergency brake assembly (82) according to claim 22 or 23, wherein the first sleeve (84a) and / or the second sleeve (84b) are injection molded on the actuating element (34).

25. The emergency brake assembly (82) according to any one of the preceding claims, wherein the length (L BE ) is smaller than the length (L) of the emergency brake unit (24) relative to the actuating element (34) BE ) in a direction parallel to the axis (A), and / or a length (L) of the actuator element (34) BE ) is completely located at the length (L) of the actuating element (34) BE ) within the dimension (A) of the emergency brake unit (24) measured in parallel.

26. The emergency brake assembly (82) according to any of the preceding claims, wherein the actuating element (34) and / or a portion of the retaining structure (35) mechanically shields a drive coupling portion of the brake element (29).

27. A method for operating an emergency brake assembly (82) having a movably mounted brake element (29), in particular a brake cam (30), for braking a cutting element of a motor-driven tool (8), wherein the emergency brake assembly (82) further comprises a linear actuating element (34), the actuating element (34) comprising a shape memory alloy (36) and the actuating element (34) being drivingly coupled to the brake element (29), the method comprising: - moving the brake element (29) by means of the actuating element (34), and - The movement coupling between the actuating element (34) and the braking element (29) is subsequently cancelled or terminated.

28. The method of claim 27, further comprising: The actuating element (34) is returned to an initial position, wherein the return occurs independently of the braking element (29).

Images